Marco Rubio, the young Cuban-American senator from Florida, has thrown down the gauntlet to his former mentor Jeb Bush in the race to become the Republican candidate for president.

The 43-year-old senator rose through the ranks of Florida politics as a protégé of Mr Bush, who was governor of the state from 1999 to 2007.

The two men were so close that as Mr Rubio considered running for the Senate in 2010 he made it clear he would step aside if Mr Bush wanted the seat for himself.

That all changed this week as Mr Rubio thrust himself into the race for the White House and into direct competition with Mr Bush, who is likely to announce his own candidacy in the coming weeks.

“I have heard some suggest that I should step aside and wait my turn. But I cannot,” Mr Rubio said. “Because I believe our very identity as an exceptional nation is at stake, and I can make a difference as president.”

Mr Rubio did not single out his former mentor by name but contrasted his own humble upbringing as the son of Cuban immigrants to “those who come from power and privilege”.

The comment appeared to be an oblique reference to Mr Bush, who is the son of a president and hails from a wealthy political dynasty that has spent decades at the top of American public life. Mr Rubio also seemed to take aim at both the 61-year-old Mr Bush and the 67-year-old Hillary Clinton as he insisted that “the time has come for our generation to lead”.

“This election is not just about what laws we will pass,” he said. “It is a generational choice about what kind of country we will be.”

While Mr Rubio is joining a crowded Republican field with candidates from all wings of the party and corners of the country, his most direct competition is with Mr Bush.

Both hail from Florida and will be fighting for the support of the same Floridian donors. Both also occupy a similar ideological space within the party: emphasising a strong military and education reforms but

not dwelling on divisive social issues, such as abortion.

The two men, who live just a few miles from each other in Miami, also share a strong connection with Florida’s Latino community. Mr Rubio’s parents fled Cuba before the 1959 revolution and their son was raised speaking both English and Spanish.

Mr Bush is married to a Mexican-American and speaks fluent Spanish after living in Venezuela in his twenties. At one point he accidentally gave his ethnicity as Latino on a voter registration form. While Mr Rubio lags behind Mr Bush in the polls, he is a formidable campaigner and some Republicans believe he would be a better candidate to take on Mrs Clinton.

His youth and immigrant background would contrast sharply with Mrs Clinton, while Mr Bush’s age and famous last name might constrain his efforts to take on the former first lady.

If he is defeated in his quest for the Republican nomination, Mr Rubio could still make an attractive candidate for vice president on the Republican ticket.

In his announcement speech in Miami, Mr Rubio presented his own life story as evidence of America’s power to grant opportunities to anyone prepared to work hard.

He described how his father worked as a bar tender in order to provide for his children, one of whom is now a US senator with ambitions for the White House.

“That journey, from behind that bar to behind this podium, is the essence of the American dream,” Mr Rubio said. He struck a hawkish note on foreign affairs, accusing President Obama of making “dangerous concessions to Iran” and of “being passive in the face of Chinese and Russian aggression”.

He said that Mr Obama and Mrs Clinton had “forgotten that when America fails to lead, global chaos inevitably follows, so they appease our enemies, betray our allies and weaken our military.”

The father-of-four called for reforms to the country’s education system and tax code that he said would help those without wealth or privilege get ahead.

‘If their American dreams become impossible, we will have become just another country, he said. “But if they succeed, the 21st century will be another American century.

“This will be the message of my campaign and the purpose of my presidency.”

The message is similar to that of Mr Bush, who has travelled across the US saying he believes in a “right to rise”, that ensures people from humble backgrounds can get ahead.